The present invention relates to mechanical face seals and in particular but not limited to seals for gases in which grooves are provided in one of the seal faces, to establish a cushion of gas between the seal faces when one seal face rotates relative to the other. The invention also relates to seals of this type for use with other fluids.
Hitherto, the grooves in such seals have normally been of helical configuration extending at an obtuse angle to the direction of rotation of the seal face. The grooves extend from one edge, part way across the seal face, a continuous annular dam formation being provided at the other edge of the seal face.
With grooves of such configuration, upon rotation of the face, fluid will move along the groove towards the end closed by the dam formation, further fluid being drawn into the open end of the groove. The closed end of the groove will impede further flow of fluid between the seal faces and will cause a build-up of pressure, forcing the seal faces apart, so that a cushion of fluid is produced between the seal faces. The grooves are designed so that the cushion of fluid will be maintained between the seal faces sufficient to prevent the faces coming into contact with one another, whilst avoiding significant leakage of fluid.
Helical grooves of the form disclosed above are however effective for relative rotation of the seal faces in only one direction, rotation of the seal faces in the other direction giving no hydrodynamic lift.
There is however a requirement for fluid seals of the type disclosed above which will act effectively for relative rotation of the seal faces in both directions.
It has been proposed to use grooved areas of triangular configuration, in which one wall of the grooved area will be inclined at an obtuse angle to the direction of rotation of the seal face, irrespective of the direction of rotation. Grooved areas of such configuration will produce lift between seal faces for relative rotation in both directions. However, as the walls of the triangular grooved areas are divergent, the number of grooved areas that may be accommodated around the circumference of the seal face will be significantly reduced in comparison to the number of helical grooves that could be accommodated. Consequently, the lift that may be produced in total between the seal faces will be significantly reduced.
The present invention provides a mechanical face seal of the type described above, with bidirectional groove profile with improved lift characteristics.
While in this specification the grooved areas are described in terms of triangular or trapezoidal configuration, it is intended that these terms should cover shapes of generally triangular or trapezoidal configuration defined by straight or curved sides.